Method of jointing electrical cables and tool therefor

ABSTRACT

For forming an electrical connection between a cable, which may be coated with a nondraining insulating material, and a ductile metal ferrule into which the cable is inserted a special compression tool is employed. The compression tool consists of a support and a punch, which tapers stepwise and is also tapered between adjacent steps so that the punch may progressively pull more metal into the depression formed by the punch and yet may be withdrawn easily from the depression.

United States Patent Morby Feb. 29, 1972 [54] METHOD OF JOINTING ELECTRICAL 3,509,608 '571970 Bennett ....29/628 CABLES AND TOOL THEREFOR 3,514,528 5/1970 Ray ....29/628 3,515,795 6/1970 Kuo ....29/628 1 lnvemorr John Edward Morby, Banbury, England 3,525,799 8/1970 Ellis ..29/628 R h [73] Assignee sllfzgec ezegzdaand Development Limited, Primary Examiner john F. Campbell Assistant Examiner-Donald P. Rooney [22] Filed: Jan. 6, 1970 Attorney-Robert S. Dunham, P. E. Henninger, Lester W. pp No: 947 glzigzyThomas F. Moran, Christopher C.'Dunham and Robert [30] Foreign Application Priority Data '[57] ABSTRACT Jan. 8, 1969 Great Britain ..l,255/69 fmming eiectrical F a l which may be coated with a nondralmng insulating material, and a ductile metal ferrule into which the cable is inserted a special [52] U.S. Cl ..29/628, 29/63l07 compression tool is employed The compression tool consists of a support and a punch, which tapers stepwise and is also [51] Int. Cl. ..l-l0lr 43/00, HOSk tapered between adjacent Steps so that the punch may [58] Field of Search ..29/628, 629, 630 A, 630 R; progressively pull more metal into the depression formed by 174/84, 94 the punch and yet may be withdrawn easily from the depression. [56] References Cited 6 Claims, 7 Drawing Figures UNITED STATES PATENTS 3,499,098 3/1970 Mcqahey ..29/628 METHOD OF JOINTING ELECTRICAL CABLES AND TOOL THEREFOR Thepresent invention relates to the formation of a compressionjoint between an electric cable and a tubular ferrule. It is well known to joint electric cables by inserting the ends of the cables to be joined into the opposite ends of a ferrule, the wall of which is then compressed or indented so as to form an electrical connection between the metal of the cable and the ferrule. While compression joints of this type have been used with many forms of insulated conductors, formed of a ductile metal, such as aluminum or copper, compression joints have been previously found unsatisfactory for forming a satisfactory electrical connection between a stranded cable of the type in which the conductors are coated or impregnated with nondraining insulating materials, and a ferrule. Such insulating materials normally contain a considerable proportion of a high-viscosity wax, which forms on the conductor surface an insulating film difficult to remove either by means of solvents or by mechanical action. Difficulties have also been experienced with insulated cables having dry, solid aluminum, sector conductors.

The present invention is therefore directed to providing a means for forming a more efficient compression joint, which leads to the breakdown of any wax film and/or oxide film on the conductor during the indenting of the ferrule to produce an electrical contact between the metal of the ferrule and the conductor of the cable. The ferrules employed for forming compression joints between aluminum conductors are themselves necessarily made of aluminum to avoid corrosion problems due to local electrolytic action. Aluminum metal is subject to'extensive plastic flow when subjected to compression between plain surfaces. It was recognized for the purpose of the present invention that a high interfacial pressure between the inner wall of the ferrule and the surface of the conductor would be necessary to break down the wax film and/or the surface oxide before metal to metal contact could be established.

Therefore the area on the external surface of the ferrule initially subjected to compression should be small so that the necessary high interfacial pressure could be developed for breakdown of the wax and/or oxide insulating layer. At the same time the method of forming the joint must be such as to minimize the metal flow from beneath the indenting punch during compression so as to create maximum interfacial pressure and to avoid the punch breaking through the wall of the ferrule. In order to satisfy this condition the present invention provides a method of forming a compression joint between a ductile metal ferrule and a cable inserted therein which comprises subjecting the wall of the ferrule to compression between a support and a punch having a flat head end and a series of surfaces arranged stepwise in relation to the head end and substantially normal to the direction of movement of the punch with the result that as the punch penetrates the ferrule, at successive intervals the surface of the ferrule is engaged by an additional plane surface, which has the effect of gripping a fresh area of the ferrule surface and drawing material into the indented recess in the ferrule wall, the sides of the punch between the successive stepped surfaces being slightly tapered to ensure easy withdrawal of the punch after the formation of the joint. The stepped indenting punch may have any convenient cross section, but for ease in manufacture it is preferably circular or rectangular (including square). When it is rectangular the punch is in the overall form of a four-sided pyramid. The stepped surfaces may be formed on one or both pairs of side faces.

In operation the relatively small tip or head end of the punch provides the high local pressure required to break down the wax and/or oxide film on the conductors, while the steps, which are parallel with the head end, grip the metal of the ferrule during the process of indentation, the frictional engagement between the successive step surfaces and the surface of the ferrule thus serving to restrict lateral flow of metal away from the area beneath the head end of the indenting punch.

An indenting tool for use in carrying out the method of the present invention comprises a frame or body, having a jaw to receive a backing die or support shaped to act as a seating for the ferrule and a holder for the indenting punch, positioned opposite the jaw and movable towards and away from the jaw. The holder for the indenting punch is preferably in the form of a piston, moving in a cylinder integral with or secured to the body and provided with an inletfor hydraulic fluid, so that the force for application to the indenting punch can be generated by means of a hydraulic pump.

The backing die is preferably removable from the jaw so that the backing die employed may be appropriate to the external diameter of the ferrule. The external diameter of the ferrule is in turn governed by the sizes of the cables to be joined. In general the ferrules have an internal diameter slightly exceeding the diameter of the conductors and have a wall thickness which varies between about 0.1 and 0.3 inches depending upon the sizes of the cables to be jointed. While the bore of the ferrule is in most cases plain, it may also be threaded so as to provide a series of sharp ridges for cutting through the wax film under the pressure of the indenting tool.

The method of the invention may be applied to the formation of compression joints between ferrules and both stranded and solid conductors. The included angle at the apex of the punch is preferably 40-70 where the cable is stranded and to 105 where the cable is solid (the included angle being taken as twice the angle at which the plane of any side of the punch lies to the vertical). The sides of the individual steps in the stepped indenting punch are themselves also slightly tapered at an angle, for example, of 515. Useful results are obtainable within a very wide range of variation of interval between successive steps. In general it may be stated that the number of steps should be not less than 5 or greater than per inch of taper. In the preferred range of 45-70 of included angle it is preferred that the depth of the successive steps should be in the range of 0.25-0.1 inch. The diameter of the tip of a conical indenting punch should preferably be in the range of 0.05 to 0.25 inch, while in the case of a punch of rectangular cross section the length may be in the range of 0.05 to l inch and the width in the range of0.05 to 0.25 inch.

A compression-type jointing tool constructed in accordance with the present invention has been utilized, employing appropriate backing dies, but only a single stepped indenting punch, with a wide range of impregnated aluminum conductor cables in the range of 0.04 to 1 square inch with highly satisfactory results.

Referring now to the accompanying drawings:

FIG. 1 is a section of a compression indenting tool for use in applying the method of the present invention,

FIG. 2 is a side view of a conical indenting punch,

FIG. 3 is a side view of a pyramidal indenting punch,

FIG. 4 is a section on the center line of the punch of FIG. 3,

FIG. 5 is a view of a compression joint made in accordance with the invention,

FIG. 6 is a longitudinal section of one form of ferrule for use in the method of the invention, and

FIG. 7 is a longitudinal section of a second form of ferrule.

The compression indenting tool shown in FIG. 1 comprises a body 1, having a jaw 2, to which a backing die or support 3 of appropriate size can be releasably secured. A cylinder 4 is secured in the body 1 and has a fluid inlet 5 for connection to a hydraulic pump for the supply of hydraulic fluid under pressure. A piston 6 is provided in the cylinder 4 and is retained by an annular retainer 7. The piston 6 carries an indenting punch 8 of the type discussed above. The punch 8 is carried in a recess in the extension 9 of the piston and is secured by a cross pin 10.

One form of indenting tool 8 is illustrated in FIG. 2 and has a shank 11, having an aperture 12 therein for engagement by pin 10. The punch has a flat tip or head surface 14, surrounded by a series of annular surfaces 15, arranged stepwise around the tip or head surface 14. The surface of the steps 16 between successive annular surfaces 15 is tapered at an angle of about 5 in relation to the axis of the punch.

1n the alternative form of punch illustrated in FIGS. 3 and 4 the tip or head end surface 24 of the punch is rectangular, having a length approximately three times its width. The included angles between the planes of the major sides 25 and the planes of the minor sides 26 are approximately equal. The sides 26 are not formed with stepped surfaces, but the sides 25 are formed with a series of straight surfaces 27, which lie in planes substantially normal to the axis of the punch, separated by steps 28, which lie at a taper angle of about to the medial plane of the punch. The surfaces and 27 need not be exactly normal to the axis of the punch but may slope inwardly or even to a slight extent outwardly without much effect on the satisfactory operation of the punch.

In use the punch of FIGS. 3 and 4 is mounted so that the surfaces 27 lie lengthwise of the ferrule. The height of the steps are chosen to be less than the thickness of the wall of the ferrule.

Two forms of ferrule for use in the method of the invention are illustrated in FIGS. 6 and 7. The ferrule 31 of FIG. 6 is in the form of a simple tube of aluminum or other ductile metal and having a wall 32 of substantial thickness, as indicated below, and a smooth bore 33. The ferrule 41 of FIG. 7 has a wall 42 and a threaded bore 43 for the reasons indicated above. The wall thickness and other dimensions of a ferrule for connecting a particular size of cable are the same for both the ferrule of FIG. 6 and the ferrule of FIG. 7.

The wall thickness of aluminum ferrules for use in connec tion with the method of the present invention may have a wall thickness varying between about 0.15 inches and about 0.30 inches, for ferrules varying between about 0.25 and l inch internal diameter, the larger the internal diameters of the ferrule requiring in general greater wall thicknesses.

A compression joint made in accordance with the invention is illustrated in FIG. 5 and may employ a ferrule of the type in either of FIG. 6 or FIG. 7. The ends of two stranded cables 44 and 45 are cleaned by brushing with a wire brush and are inserted into a ferrule 31 of appropriate interior diameter and the wall of the ferrule is deformed by means of the indenting tool already described as indicated at 46. In forming the compression joint, the wall of the ferrule should be indented in the case of a stranded cable, as indicated in FIG. 5, for a distance approximating to half the external diameter of the ferrule and to a lesser extent where the conductor is solid, although no hard and fast rule can be laid down.

I claim:

1. A method of forming a compression joint between a ductile metal ferrule and a cable inserted therein, by indentation of the ferrule, which comprises:

A. forming an initial indentation of the ferrule wall by pressing a flat head surface of a punch into said ductile metal at a selected outer surface portion thereof; and

B. progressively increasing said indentation by l. maintaining pressure of said punch head surface for movement inward of the ferrule, while 2. gripping fresh areas of the ferrule and drawing metal thereof into the region undergoing indentation, by a. successively engaging further outer surface portions of the ferrule lying in succession near said first surface portion and each other, by correspondingly successive additional punch surfaces lying substantially normal to the direction of movement of said punch head surface and laterally and longitudinally displaced in relation to said head surface and to preceding punch surfaces, and b. maintaining pressure of each said additional punch surface for movement inward of the ferrule, after the said engagement of each said additional punch surface with the ferrule surface.

2. A method according to claim 1 which includes successively engaging the metal of the ferrule with surfaces extending longitudinally inward of the indentation in the successive longitudinal spaces among the head and additional punch surfaces, said longitudinal surfaces being tapered toward said head Kunch surface.

3. method according to claim 2 in which said successively engaged longitudinal surfaces are tapered at an angle of 5 to 15 to the direction of movement of the head and additional punch surfaces into the indentation.

4. A method according to claim 1 in which said head and additional punch surfaces are circular and disposed concentrically stepwise, said successive engagements and pressure of said surfaces being effected to produce an indentation substantially circular in cross section.

5. A method according to claim 1 in which said head punch surface is rectangular and said additional punch surfaces in clude surfaces that lie along lines parallel to two opposite sides of said head surface and are disposed in stepwise relation constituting the major sides of a four-sided pyramid that is elongated in plan, said successive engagements and pressure of said surfaces being effected to produce an indentation of substantially pyramidal shape.

6. A method according to claim 1 for forming said joint between the ferrule and a stranded conductor constituting said cable, which includes continuing said progressive increasing of said indentation, to indent the ferrule wall by a distance equal to approximately half the external diameter of the ferrule.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION patent 3,644,989 Dated' February 29, 1972 JOHN EDWARD MORBY Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' In the heading "and abstract page, address ofassignee .should read Montreal;- before "Quebec" Col. 2, 'line 36, for 0.25 read --0.025-- Singed and seal this 15th day of August 1972.

(SEAL) Attest:

EDWARD M. FLETCHER, JR I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PQ'WSO utcoMM-oc wan-Poo ".5. GOVIINMENT [III'ING OIHCI: IQ! 0-JlG-J3Q UNITED STATES PATENT OFEICE CERTIFICATE OF CORRECTION 3,644,989 Dated February 29, 1972 JOHN EDWARD MORBY Patent No.

Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading and abstract page, address of essignee .should read --Montrea1,-- before "Quebec" Col. 2, 'line 36, for 0.25 read --0.025-

Singed and seal this 15th day of August 1972.

(SEAL) Attest:

EDWARD M. FLETCHER, JR I ROBERT GOTTSCHALK Commissioner of Patents Attesting Officer ulcoMM-oc Man-Poe I 0.5. GOVIINIENY [RIITING OHICI: "69 0-356-834 FORM PQ-1050(10-69) 

1. A method of forming a compression joint between a ductile metal ferrule and a cable inserted therein, by indentation of the ferrule, which comprises: A. forming an initial indentation of the ferrule wall by pressing a flat head surface of a punch into said ductile metal at a selected outer surface portion thereof; and B. progressively increasing said indentation by
 1. maintaining pressure of said punch head surface for movement inward of the ferrule, while
 2. gripping fresh areas of the ferrule and drawing metal thereof into the region undergoing indentation, by a. successively engaging further outer surface portions of the ferrule lying in succession near said first surface portion and each other, by correspondingly successive additional punch surfaces lying substantially normal to the direction of movement of said punch head surface and laterally and longitudinally displaced in relation to said head surface and to preceding punch surfaces, and b. maintaining pressure of each said additional punch surface for movement inward of the ferrule, after the said engagement of each said additional punch surface with the ferrule surface.
 2. gripping fresh areas of the ferrule and drawing metal thereof into the region undergoing indentation, by a. successively engaging further outer surface portions of the ferrule lying in succession near said first surface portion and each other, by correspondingly successive additional punch surfaces lying substantially normal to the direction of movement of said punch head surface and laterally and longitudinally displaced in relation to said head surface and to preceding punch surfaces, and b. maintaining pressure of each said additional punch surface for movement inward of the ferrule, after the said engagement of each said additional punch surface with the ferrule surface.
 2. A method according to claim 1 which includes successively engaging the metal of the ferrule with surfaces extending longitudinally inward of the indentation in the successive longitudinal spaces among the head and additional punch surfaces, said longitudinal surfaces being tapered toward said head punch surface.
 3. A method according to claim 2 in which said successively engaged longitudinal surfaces are tapered at an angle of 5* to 15* to the direction of movement of the head and additional punch surfaces into the indentation.
 4. A method according to claim 1 in which said head and additional punch surfaces are circular and disposed concentrically stepwise, said successive engagements and pressure of said surfaces being effected to produce an indentation substantially circular in cross section.
 5. A method according to claim 1 in which said head punch surface is rectangular and said additional punch surfaces include surfaces that lie along lines parallel to two opposite sides of said head surface and are disposed in stepwise relation constituting the major sides of a four-sided pyramid that is elongated in plan, said successive engagements and pressure of said surfaces being effected to produce an indentation of substantially pyramidal shape.
 6. A method according to claim 1 for forming said joint between the ferrule and a stranded conductor constituting said cable, which includes continuing said progressive increasing of said indentation, to indent the ferrule wall by a distance equal to approximately half the external diameter of the ferrule. 